Pregnancy - small for dates Flashcards
What are the 2 primary causes of a small baby ?
- Pre-term birth (so normal for their gestation, its just that they are young)
- Small for gestational age (SGA)
Define what pre-term delivery is and the 3 sub-classifications of it
Defined as delivery between 24 & 36+6 weeks:
- Extreme preterm: 24 – 27+6 weeks
- Very preterm: 28 – 31+6 weeks
- Moderate to late preterm: 32 – 36+6 weeks
What happens to the survival rate of pre-term pregnancies as they decrease in prematurity i.e. get older
- Survival rate increases the less premature they are
- Beyond 32 weeks >95% survival
List the causes of pre-term delivery
- Infection
- ‘Over distension’; Multiple pregnancy, polyhyraminos
- Vascular; Placental abruption
- Intercurrent illness; Pyelonephritis / UTI, Appendicitis, Pneumonia
- Cervical incompetence - cervix dilates before pregnancy has reached term
- Idiopathic (unknown)
List the risk factors for pre-term birth and highlight the 2 main ones to know about
- Previous Pre-term labour (20% risk X1; 40% X2))
- Multiple (50% risk)
- Uterine anomalies
- Age (teenagers)
- Parity (=0 or >5)
- Ethnicity
- Poor socio-economic status
- Smoking
- Drugs (especially cocaine)
- Low BMI (<20)
what are the 4 main ways pre-term labour presents ?
- 25% planned caesarean section - Severe pre-eclampsia, kidney disease or poor fetal development.
- 20% premature rupture of membranes (PROM)
- 25% emergency event - Placental abruption, infection, eclampsia
- 40% cause unknown
What are the symptoms suggestive of pre-term labour ?
- Contractions
- Rupture of membranes (can happen a fair bit before labour starts)
- Brownish or blood tinged mucus discharge
How is PROM diagnosed ?
- 1st line = Speculum exammination - if amniotic fluid pooling seen offer management, if none seen then:
- 2nd line = Consider performing insulin like growth factor binding protein-1 test or placental alpha-microglobulin test of vaginal fluid
If both +ve then give antibiotics, if only insulin or placental alpha test +ve then consider their clinical condition & if neither +ve then reassure PROM is unlikely
If PROM suspected and labour has already been established, should you carry out the diagnostic tests for PROM?
No
What is the management of PROM?
- 80% of PROM will initiate labour but in 20% it will not & may take a while before labour starts
- If labour has initiated then management is that of pre-term labour
- If labour does not initiate then there is now a risk of developing infection (due to ceale being broken) ==> antibiotics are given
What antibiotics are given for PROM when labour has not initiated ?
- 1st line = erythromycin (max 10 days until labour established)
- 2nd line = penicillin (if erythro not tolerated)
What is the management options for cervical incompentence ?
- For women between 16 to 27+6 weeks with a dilated & exposed, unruptured fetal membranes a rescue cervical cerclage (cervical stitch) can be done
- Contraindicated if signs of infection, active vaginal bleeding or uterine contractions
Does initiations of contractions always lead to pre-term labour ?
No - in 50% of cases contractions cease spontaneously & treating the cause e.g. pylonephritis may make it cease
What is the management of pre-term labour ?
Treat underlying cause if possible e.g. pylonephritis and it may cease
Give glucocortiocosteroids - for all at risk of iatrogenic or spontaneous pre-term birth between 24 & 34+6 weeks and consider for suspected or established pre-term labour, those having elective pre-term birth or who have prelabour PROM between 24 & 35+6 weeks (note need roughly 24hrs to work prior to the actual delivery)
Tocolytics (anti-contraction drugs) - for pregnancy with intact membranes & are in suspected or diagnosed preterm labour:
- 1st line = nifedipine
- 2nd line = oxytocin receptor antagnosit e.g. atosiban if nifedipine contraindicated
IV Magnesium sulphate (MgSO4) - for neuroptoection of baby when in established pre-term labour or having a planned one within 24hrs between 24 & 33+6 weeks
When is use of nifedipine contraindicated for pre-term labour ?
If the women has heart disease
What are the side effects of nifedipine ?
- Decreased BP
- Facial flushing
- Headache
- Increased pulse
- Very rarley MI
Why is it important to differentiate between babies who are premature and those who are SGA, why?
Because they are at risk for different problems following birth
What are the 2 causes of a baby being small for their gestational age (SGA)?
- Intra-uterine growth restriction (IUGR) - this is pathological
- Baby is constitutinally small (familial)
Define what small for gestational age (SGA) is
This is an infant with a birthweight that is less than the 10th centile for their gestation when compared to general population & customised growth charts (corrected for maternal height, weight, fetal sex & birth order)
Define what low birth weight is
LBW = birth weight below 2.5 kg (regardless of gestation)
What can IUGR broadly speaking be due to problems with what 3 main things ?
- Maternal
- Fetal
- Placental
What maternal factors can lead to IUGR ?
- Lifestyle; Smoking, Alcohol, Drugs
- Height and weight - BMI < 20
- Age ≥ 40
- Maternal disease e.g. HTN, renal impairment, DM, PET
What fetal factors can lead to IUGR ?
- Infection e.g. Rubella, CMV, toxoplasma
- Congenital anomalies e.g. absent kidneys
- Chromosomal abnormalities e.g. Downs syndrome
What placental factors can lead to IUGR ?
- Infarcts
- Abruption
- Often secondary to HTN
IUGR implies a pathological restriction of the genetic growth potential of a fetus, as a result IUGR fetuses may manifest evidence of fetal compromise which may be indicated by what?
- Abnormal doppler studies
- Decreased liquor volume
What are the potential consequences of IUGR ?
- Antenatally/ in labour - risk of hypoxia &/or death
Postnatally:
- Hypoglycaemia
- Effects of asphyxia
- Hypothermia
- Polycythaemia
- Hyperbilirubinaemia
- Abnormal neurodevelopment
What are the clinical features suggestive of IUGR ?
- Predisposing factors
- SFH < than expected
- Reduced liquor (oligohyraminos)
- Reduced fetal movements
What is done to assess fetal wellbeing (survellience of a SGA baby)?
- Assessment of growth
- CTG
- Doppler US
Biophysical profile (now not done)
How is the growth of a fetus assessed ?
- Initially use SFH and plot measurements against centile charts at each antenatal appointement from 24 weeks
- If growth restriction suspected (AC or EFW below the 10th centile) then monitor growth with serial U/S of head & abdominal circumference
How is a CTG assessed in the assessment of a SGA ?
DR C BRAVADO - covered in another lecture
Serial growth scans and CTG are used in the assessment of a SGA baby but what is the primary survellience tool?
Umbilical artery doppler (middle cerebral artery doppler & ductus venous suppler also used) - it is used to measure placental resistance to blood flow
Go over these points on US assessment of a SGA baby
- Umbilical artery should be low resistance but if compromised becomes high resistance, so flow becomes absent or even reversed in diastole.
- Ductus venosus becomes pulsatile and increases its resistance.
- Middle cerebral artey decreases its resistence to maintain blood flow to fetal brain.
When should a SGA baby be delivered ?
If all well deliver by 37 weeks
Indications for considering earlier delivery by caesarean section:
- Growth becomes static (IOL may be appropriate)
- Abnormal umbilical artery Doppler
- Normal umbilical artery Doppler with abnormal MCA between 32 and 37 weeks
- Abnormal umbilical artery Doppler with abnormal ductus venosus Doppler between 24-32 weeks
Note - Delivery of the SGA infant is a balance between the risks of prematurity and the potential of hypoxia in utero or still birth.
